One of the most difficult problems to overcome in the field of fusible interfacing is the risk of penetrating the interfacing support when hot pressing the fusible interfacing against the piece of apparel to be reinforced. The temperature selected to carry out that hot pressing must melt the polymer dot so that the molten polymer can spread and adhere to the fibers or filaments on the surface of the piece of apparel. However, spreading does not always occur just on the surface, and the molten polymer flows through the fibers or filaments and appears on the opposite face of the interfacing support. This does not cause a problem as regards appearance unless the interfacing is intended to be visible and to form the right side of the garment. In all cases, that penetration locally increases the stiffness of the interfacing and thus of the piece of apparel, which can be contrary to the desired effect. It can also adhere to backing fabric such as linings and cloth facings, which has a deleterious effect on the quality of the garment.
To overcome this difficulty, a fusible interfacing wherein the dots of hot-melt polymer comprise two superimposed layers has already been proposed; a first layer is in contact with the right side of the interfacing support and a second layer is disposed in precise alignment over the first. Clearly, the constituents of the two layers are determined so that during application with heat pressure to the piece of apparel, only the hot-melt polymer of the second layer reacts under the action of heat. In that case, the hot-melt polymer can only spread towards the piece of apparel, and is prevented from spreading towards the interfacing support as the first layer acts as a kind of barrier.
In practice, that technique of two superimposed layers has disadvantages, in particular problems with superimposing the two layers and a risk of delaminating the two layers.
To overcome the above disadvantages, the Applicant has already proposed, in French patent FR-A-2 606 603, the use of means of a chemical nature acting on the hot-melt polymer to modify its chemical structure at least partially at least at the interface with the interfacing support, to prevent the hot-melt polymer from adhering through the interfacing support under the effect of heat and/or pressure and/or steam. The means of a chemical nature that can modify the chemical structure of the hot-melt polymer comprise at least one reactive substance and at least one reactive means that can initiate, ensure, and encourage the reaction between the reactive substance and the hot-melt polymer.
Contact between the reactive substance and the hot-melt polymer is made either by mixing those two elements, which are then deposited as an intimate mixture, in the form of dots, on the interfacing support, or by applying the reactive substance to the interfacing support before depositing dots of polymer (which are then free of reactive substance). Heat sources, ultraviolet radiation and electron bombardment are cited amount the reactive means.
The Applicant has also proposed, in European patent EP-A1-0 855 146, a method in which dots of hot-melt polymers with a mean thickness E and containing a radical activator are deposited on the right side of an interfacing support and one of the faces of the support undergoes electron bombardment, adjusting the penetration depth of the electrons into the dots of hot-melt polymer to produce a modification in the physico-chemical properties of the hot-melt polymer selected from the melting point and the viscosity over a thickness e with respect to the mean thickness E.
The radical activator creates free radicals that can initiate self-polymerization of the hot-melt polymer. Thus, it does not strictly concern a reactive substance as envisaged in FR-A-2 606 603.
The techniques taught by the two documents cited above have a variety of disadvantages. In FR-A-2 606 603, when the reactive substance is applied to the interfacing support before depositing the polymer dots, the reaction that occurs after providing heat, UV irradiation or electron bombardment occurs at the interface between the reactive substance and the hot-melt polymer. This reaction thus only occurs over a much reduced thickness. In all the other cases the reactive substance of FR-A-2 606 603 or the radical agent of EP-A1-0 855 146 is mixed with the hot-melt polymer prior to depositing dots on the interfacing support. That mixture is normally produced when the polymer is dispersed in the form of a paste, the reactive substance or radical agent then being incorporated like any other product of the formulation. To obtain a more intimate mixture, according to EP-A1-0 855 146, the hot-melt polymer and radical activator are first mixed, then the mixture undergoes the successive operations of fusion, extrusion and grinding to obtain a powder that is used as it is for coating or diluted for subsequent preparation of an aqueous dispersion in the form of a paste to deposit dots of polymer on the interfacing support. However, regardless of the intimate nature of the mixture, each dot applied to said interfacing support has a heat fusible polymer that provides the adhesive function which is required to adhere the interfacing support to the piece of apparel to be reinforced, and a reactive substance or a radical agent which provides the reactivity function under the action of reactive means such as a heat source, UV irradiation or electron bombardment, this latter being of particular relevance to a radical agent.
In the particular case of a method of producing a fusible interfacing using electron bombardment to modify the chemical structure of the hot-melt polymer, the presence of a radical agent causes a certain number of difficulties. When the technique for depositing polymer dots employs an aqueous dispersion in the form of a paste, the components of the paste formulation have to be soluble in water for the paste to be stable over time. However, most products that are suitable radical agents are insoluble in water, at least in the proportions in which they are used to prepare the aqueous dispersion, which can cause relative instability of the paste over time. Further, products that are suitable as radical agents are generally in the form of a liquid, with boiling points that may be incompatible with the temperatures used under the operating conditions employed when depositing dots on the interfacing support. In that case, some of the radical agent may evaporate, which causes a loss in or even disappearance of the reactivity to electron bombardment. Finally, it has also been observed that, because products that are suitable as radical agents are generally low molecular weight monomers, their behavior in a mixture with a hot-melt polymer is compatible with that of a plasticizer. That behavior can involve a change in the melt viscosity of the hot-melt polymer, it can cause problems as regards the quality or with coating, and it can also change the intrinsic mechanical strength of the polymer and thus influence adhesion performance.